Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $57.33   12.187%   $64.3168   $64.32   $64.30   $64.30  
  Purchase #2 $40.28   4.270%   $42   $42.00   $42.00   $42.00  
  Purchase #3 $93.57   4.615%   $97.8883   $97.89   $97.90   $97.90  
  Purchase #4 $244.60   3.404%   $252.9262   $252.93   $252.95   $252.90  
  Purchase #5 $180.79   12.345%   $203.1085   $203.11   $203.10   $203.10  
  Purchase #6 $32.80   3.428%   $33.9244   $33.92   $33.90   $33.90  
  Purchase #7 $53.25   10.119%   $58.6384   $58.64   $58.65   $58.60  
  7 purchase totals = $702.62       $752.8026   $752.81   $752.80   $752.70